Day 9 done

day9/Cargo.lock

@@ -5,21 +5,3 @@ version = 3
 [[package]]
 name = "day9"
 version = "0.1.0"
-dependencies = [
- "itertools",
-]
-
-[[package]]
-name = "either"
-version = "1.8.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "90e5c1c8368803113bf0c9584fc495a58b86dc8a29edbf8fe877d21d9507e797"
-
-[[package]]
-name = "itertools"
-version = "0.10.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b0fd2260e829bddf4cb6ea802289de2f86d6a7a690192fbe91b3f46e0f2c8473"
-dependencies = [
- "either",
-]

day9/Cargo.toml

@@ -6,4 +6,3 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-itertools = "0.10.5"

day9/src/main.rs

@@ -1,4 +1,4 @@
-use itertools::Itertools;
+use std::collections::HashSet;
 use std::fs::File;
 use std::io::{prelude::*, BufReader};
 
@@ -7,8 +7,13 @@ fn main() -> std::io::Result<()> {
     let file = File::open("input")?;
     let reader = BufReader::new(file);
 
-    let mut tail_pos: Vec<(i32, i32)> = vec![(0, 0)];
+    let mut snake = vec![(0_i32, 0_i32); 10];
-    let mut head_pos: Vec<(i32, i32)> = vec![(0, 0)];
+    let mut visited: Vec<HashSet<(i32, i32)>> = vec![HashSet::new(); 10];
+
+    //intialize the visited
+    snake.iter().enumerate().for_each(|(i, x)| {
+        visited[i].insert(*x);
+    });
 
     //read in input
     reader.lines().for_each(|line| {
@@ -18,8 +23,7 @@ fn main() -> std::io::Result<()> {
             _ => panic!("failed parseing line {}", line),
         };
         for _ in 0..steps {
-            let (mut cur_head_x, mut cur_head_y) = head_pos.last().unwrap();
+            let (mut cur_head_x, mut cur_head_y) = snake[0];
-            let (mut cur_tail_x, mut cur_tail_y) = tail_pos.last().unwrap();
             match direction {
                 "L" => cur_head_x -= 1,
                 "R" => cur_head_x += 1,
@@ -27,37 +31,37 @@ fn main() -> std::io::Result<()> {
                 "D" => cur_head_y -= 1,
                 x => panic!("invalid movement {}", x),
             };
-            let x_offset = cur_head_x - cur_tail_x;
+            let new_head_pos = (cur_head_x, cur_head_y);
-            let y_offset = cur_head_y - cur_tail_y;
+            snake[0] = new_head_pos;
-            if x_offset > 1 {
+            visited[0].insert(new_head_pos);
-                if y_offset != 0 {
+            for i in 1..snake.len() {
-                    cur_tail_y = cur_head_y;
+                let (cur_head_x, cur_head_y) = snake[i - 1];
+                let mut new_pos = snake[i];
+                let (cur_tail_x, cur_tail_y) = new_pos;
+                let mut x_offset = cur_head_x - cur_tail_x;
+                let mut y_offset = cur_head_y - cur_tail_y;
+                if std::cmp::max(x_offset.abs(), y_offset.abs()) > 1 {
+                    if y_offset.abs() >= 2 && x_offset == 0 {
+                        y_offset = y_offset.clamp(-1, 1);
+                    } else if x_offset.abs() > 2 && y_offset == 0 {
+                        x_offset = x_offset.clamp(-1, 1);
+                    } else if x_offset.abs() > 1 || y_offset.abs() > 1 {
+                        x_offset = x_offset.clamp(-1, 1);
+                        y_offset = y_offset.clamp(-1, 1);
+                    } else {
+                        x_offset = 0;
+                        y_offset = 0;
+                    }
+                    new_pos = (cur_tail_x + x_offset, cur_tail_y + y_offset);
                 }
-                cur_tail_x += 1
+                snake[i] = new_pos;
-            } else if x_offset < -1 {
+                visited[i].insert(new_pos);
-                if y_offset != 0 {
-                    cur_tail_y = cur_head_y;
-                }
-                cur_tail_x -= 1
-            } else if y_offset > 1 {
-                if x_offset != 0 {
-                    cur_tail_x = cur_head_x;
-                }
-                cur_tail_y += 1
-            } else if y_offset < -1 {
-                if x_offset != 0 {
-                    cur_tail_x = cur_head_x;
-                }
-                cur_tail_y -= 1
             }
-            let new_tail = (cur_tail_x, cur_tail_y);
-            if *tail_pos.last().unwrap() != new_tail {
-                tail_pos.push(new_tail);
-            }
-            head_pos.push((cur_head_x, cur_head_y));
         }
     });
-    let part1 = tail_pos.iter().unique().count();
+    let part1 = visited[1].len();
     println!("Part 1: {}", part1);
+    let part2 = visited[9].len();
+    println!("Part 2: {}", part2);
     Ok(())
 }